A、From sulfur dioxide and water vapor. B、From sulfur dioxide and nitrogen oxide. C、From nitric acid and sulfur dioxide. D、From w

M: You know, everyone today is concerned about pollution. You see, the environment today is worse than years ago and we should pay attention to this or we’ll be faced with adverse results. And scientists are talking a lot about one kind of pollution, acid rain. Have you ever heard of it before?
W: Why exactly is it called acid rain? I am curious about it. Tell me something about it.
M: The reason why it’s called acid rain is because the rain or some other kind of precipitation has been polluted with acid.
W: Where does the acid come from anyway? How can this happen?
M: From cars or factories, anything that burns coal or oil. These are made up mostly of sulfur dioxide and nitrogen oxides, which react with water vapor to form sulfuric acid or nitric acid.
W: You mean that when coal or oil is burned, acid gets formed. And when it rains or snows, the acid falls back on the earth? It’s terrible.
M: Exactly. What you said is right. That’s why it’s so dangerous. Acid rain has been falling over areas of northern America and northern Europe, and if it isn’t checked, the effect on the water supply and plant and animal life could be disastrous.
W: This is something I should read more about. I really don’t know what you’ve told me. It seems to be a very serious matter.
27. What is the best topic of this conversation?
28. What energy sources cause acid rain?
29. How is sulfuric acid formed?
30. According to the man, where is acid rain a problem?